The present invention relates to a refrigerator such as a split Stirling type refrigerator in which a movable member is driven reciprocally by a pressure difference between opposite ends of the movable member.
FIGS. 7(A) to 7(D) show an operation of a conventional refrigerator such as disclosed in Japanese Patent Application Laid-Open No. 73873/1982. This refrigerator includes a reciprocal compressor 1 and a cold finger portion 2. A piston 3 of the compressor 1 serves to pressurize coolant gas such as helium to cause a pressure variation in sinusoidal form. A pressure variation in a compression chamber or space 4 is transmitted through a supply tube 5 into the cold finger portion 2. A cylindrical movable member 7 reciprocates freely in a housing 6 of the cold finger portion 2 to change volumes of a hot chamber or space 8 and a cold chamber or space 9 of the cold finger portion 2. The movable member 7 includes a regenerative type heat exchanger 10. The heat exchanger 10 is in the form of cylinder constituted with a stack of several hundreds of metal screen discs of fine mesh. Other heat exchanger such as formed by a pile of balls may be used instead thereof. Helium flows freely between the hot space 8 and the cold space 9 through the heat exchanger 10. A piston member 11 which is integral with the movable member 7 extends into a gas spring chamber or space 12 formed at an end of the hot space 8.
As shown, the refrigerator includes a pair of pressurized gas chambers or spaces separated from each other. Gas portions in the compression space 4 of the compressor 1, the supply pipe 5, the hot space 8, the cold space 9 and the heat exchanger 10 form a working chamber or space. Another gas chamber or space is formed by the gas spring space 12. The gas spring space 12 is sealed with respect to the working space by a piston seal 13 surrounding the piston member 11. A seal 14 is provided on the movable member 7 so that gas portion moving between the hot space 8 and the cold space 9 is forced to pass through the heat exchanger 10. A seal 15 is provided on the piston 3 to seal between the working space filled with gas and a buffer chamber or space in which a crank mechanism (not shown) is housed.
In operation, a lower end of the movable member 7 is in the cold space 9 of the cold finger portion 2 in a cycle shown in FIG. 7(A) and the compressor 1 is compressing gas in the working space. The compressing operation of the piston 3 of the compressor 1 causes gas pressure in the working space to increase from a minimum pressure to a maximum pressure. In this case, pressure in the spring space 12 is in a stable level between a minimum and a maximum pressures. Thus, pressure in the working space which is increasing at a certain time produces a pressure difference across the piston member 11 which is large enough to overcome frictional resistance given by the seals 14 and 13. Therefore, the piston member 11 and the movable member 7 are raised rapidly to positions shown in FIG. 7(B). Upon this movement of the movable member 7, high pressure gas in the hot space 8 at substantially environment temperature is forcibly introduced through the heat exchanger 10 into the cold space 9. The heat exchanger 10 absorbs heat of this pressurized gas passing therethrough to cool it. Therefore, with the sinusoidal driving by the crank mechanism, not shown, the piston 3 of the compressor starts to expand the working space as shown in FIG. 7(C), upon which high pressure helium gas in the cold space 9 is further cooled. This cooling in the cold space 9 provides a cooling effect large enough to produce a temperature gradient of 200.degree. K. or more along the full length of the heat exchanger 10. At a certain time during the expansion movement of the piston 3, pressure in the working space is lowered below the pressure of the spring space 12 and a pressure difference therebetween acts to the piston member 11 to an extent enough to overcome friction force caused by the seals. Therefore, the movable member 7 is driven downwardly to a position shown in FIG. 7(D). The position in FIG. 7(D) is a start position prior to the position shown in FIG. 7(A). In this state, cooled gas in the cold space 9 passes through the heat exchanger 10 to cool it, i.e., to be heated thereby, and gas heated to substantially environment temperature is returned to the hot space 8.
As is clear from the foregoing description, in order to increase the efficiency of refrigerator, the upward movement of the movable member 7 should be delayed until the piston 3 of the compressor reaches an end point of its stroke as shown in Figs. 7(A) and 7(B). Similarly, the downward movement of the movable member 7 should be delayed until the piston 3 reaches the other end of its stroke as shown in FIGS. 7(C) and 7(D). This is because cooling effect of expansion and heating effect of compression are maximum and minimum at these points, respectively. Japanese Patent Application Laid-Open No. 265459/1986 discloses an improvement of the conventional refrigerator mentioned above. However, in both of the conventional refrigerator, a phase relation between pressure in the working space and movement of the movable member is determined by only frictional force applied by the seals to the movable member, pressure loss of the heat exchanger 10, spring constant of the gas spring in the gas spring space 12 and mass of the movable member 7. Therefore, it is very difficult to obtain an optimum phase difference and to increase the efficiency of refrigerator. Further, due to non-linearity of gas spring, a center position of vibration of the movable member is influenced largely by a small change of operating condition, so that the movable member may collide the housing wall, causing the performance thereof unstable.